1. Field of the Invention
The present invention relates to polyoxazolidone resins, and more specifically, to epoxy-terminated oxazolidone resins derived from divinylarene dioxides and polyisocyanates; and polymers prepared from such epoxy-terminated oxazolidone resins.
2. Description of Background and Related Art
Epoxy terminated oxazolidone resins are known in the art and are known to be useful precursors for coatings, laminates and other uses. For example, U.S. Pat. No. 5,112,932 discloses a process for making epoxy-terminated oxazolidones by reacting a conventional epoxy resin with a polyisocyanate.
U.S. Pat. No. 5,112,932 describes epoxy oxazolidone resins prepared from epoxy resins and polyisocyanates, but does not teach the use of divinylarene dioxides as precursors for epoxy oxazolidone resins.
Braun, Dietrich; Weinert, Johann; Angewandte Makromolekulare Chemie (1979), 78, 1-19, describe the preparation of polyoxazolidones from diepoxides and diisocyanates, but does not prepare epoxy-functional polymers.
Braun, Dietrich; Weinert, Johann; Liebigs Annalen der Chemie (1979), (2), 200-9, describe the preparation of mono- and bis-oxazolidones from mono- and diepoxides and monoisocyanates, but does not use polyisocyanates and does not prepare epoxy-functional polymers.
A problem encountered with the use of prior art epoxy-terminated oxazolidone resins relates to their relatively high melt viscosity relative to their glass transition temperature (Tg). For example, D.E.R.™ 6508 epoxy-oxazolidone resin from The Dow Chemical Company has a Tg of about 45° C., which is high enough to prevent solid agglomeration or sintering, and the temperature required for its melt viscosity to equal 500 Pa-s, a melt viscosity suitable for many epoxy thermoset applications such as coatings and composites, is about 191° C. Such high processing temperatures are energy-intensive and can cause premature crosslinking in thermoset formulations.
Another problem is encountered with the use of prior art processes for the preparation of epoxy oxazolidone resins derived from divinylarene dioxides which is low selectivity to oxazolidone (e.g. less than about 40%). Side reactions can produce in addition to the desired oxazolidone substantial amounts of either isocyanurates (from isocyanate trimerization) or carbamates (from the reaction of epoxide-based alcohols and isocyanates), or both. The presence of isocyanurates increases viscosity and causes premature gelation (either during its preparation or curing). The presence of carbamates decreases the thermal stability of the derived thermoset. These side reactions commonly reduce the oxazolidone selectivity to less than about 40%.